High-frequency apparatus having two work-engaging electrodes and one adjustable electrode



c. E. ELLSWORTH 2.504,969

ENGAGING ELECTRODES AND ONE ADJUSTABLE ELECTRODE April 25, 1950 HIGH-FREQUENCY APPARATUS HAVING TWO WORK 9 Sheets-Sheet 1 Filed July 6, 1946 INVENTOR 54A; 1.. 445H/0/P77/ ATTORNEYS April 25, 1950 c. E. ELLSWORTH 2,504, HIGH-FREQUENCY APPARATUS HAVING TWO WORK-ENGAGING ELECTRODES AND ONE ADJUSTABLE ELECTRODE Filed July 6, 1946 9 Sheets-Sheet 2 INVENTOR ATTORNEYS April 25, 1950 HIGH-FREQUENCY APPARATUS HAVING TWO WORK-ENGAGING Filed July 6, 1946 c. E. ELLSWORTH 2,504,969

ELECTRODES AND ONE ADJUSTABLE ELECTRODE 9 Sheets-Sheet 5 Fig.3.

j INVENTOR ATTORN EYS April 25, 1950 C. HIGH-FREQUENCY APPARATUS HAVING TWO WORK-ENGAGING E. ELLSWORTH 2,504,969

ELECTRODES AND ONE ADJUSTABLE ELECTRODE Filed July 6, 1946 9 Sheets-Sheet 4 Tiq.5.

TE .E.

ATTORNEYS April 25, 1950 c. E. ELLSWORTH ,9

HIGH-FREQUENCY APPARATUS HAVING TWO WORK-ENGAGING ELECTRODES AND ONE ADJUSTABLE ELECTRODE Filed July e, 1946 9 Sheets-Sheet 5 lNVENTOR April 25, 1950 c. E. ELLSWORTH 0 6 HIGH-FREQUENCY APPARATUS HAVING TWO WORK-ENGAGING ELECTRODES AND ONE ADJUSTABLE ELECTRODE Filed July 6, 1946 9 Sheets-Sheet 6 ATTORNEYS April 25, 1950 c. E. ELLSWORTH 2,504,

A HIGH-FREQUENCY APPARATUS HAVING Two WORK-ENGAGING ELECTRODES AND oNE ADJUSTABLE ELECTRODE Filed July 6, 1946 I 9 Sheets-Sheet 7 l6 l6 Tia lz L. .i.

/5/ Ti lE-E.

/ INVENTOR 64/74 5.5 Lf/VUATH ATTORNEYS April 25, 1950 HIGH-FREQUENCY AEPARATUS HAVING TWO WORK-ENGAGING c E. ELLSWORTH 2,504,969

ELECTRODES AND ONE ADJUSTABLE ELECTRODE Filed July 6, 1946 9 Sheets-Sheet 9 205' g ma ATTORNEYS Patented Apr. 25, 1950 HIGH-FREQUEN CY APPARATUS HAVING TWO WORK-ENGAGING ELECTRODES AND (ENE ADJUSTABLE ELECTRODE Carl E. Ellsworth, Louisville, Ky., assignor to The Girolier Corporation, Louisville, Ky., a corporation of Delaware Application July 6, 1946, Serial No. 681,664

20 Claims. i

This invention relates to high-frequency treating systems for dielectric materials and has for an object the provision of means not only of applying pressure to the load or to the dielectric material undergoing treatment but also for regulating the amount of electrical power or energy applied to or absorbed by said material.

It has heretofore been recognized that dielectric materials change their characteristics with increasing temperature. The power factor and dielectric constant of many materials increase as the temperature rises. In accordance with the disclosure of a co-pending application, filed May 31, 1946, Serial Number 673,296, of W. L. Atwood, and assigned to the same assignee as the present invention, the dielectric material undergoing treatment may be disposed between two electrodes for application of pressure thereto,while .a third electrode may be adjusted in a manner to produce a predetermined application of power to the material. While the system or arrangement -of said Atwood application is believed to represent an improvement in the art, the present invention is a further improvement as regards both simplification of structure and flexibility of operation.

In carrying out the present invention in one form thereof, there may be applied to the dielecztric material to be heated a uniform pressure of a predetermined magnitude which will be maintained. constant during the heating of said mate- :rial. The pressure-applying mechanism is separate from the mechanism for varying the tuning, or position of a control electrode, by means of which the voltage applied to the dielectric material may be changed. For some conditions of operation, the pressure-applying means may be rendered ineffective and. the dielectric material may be heated in the absence of pressure or with an air space between it and one of the two electrodes between which the high-frequency energy is applied.

The present invention includes additional features of arrangement and constructional combinations and subcombinations, a detailed description of which, together with other objects and advantages of the invention, may be best set forth in the following detailed description taken in con junction with the accompanying drawings, in which:

Fig. 1 is a fractional sectional view of one form of apparatus embodying the invention;

Fig. 1--A is a fractional side view, partly in section, illustrating the manner in which the pressure-applying lever of Fig. 1 may be made effective or ineffective;

Fig. 2 is a fractional sectional view, taken on the line 2-2 of Fig. 5, of another apparatus embodying the invention;

Fig. 2-A is an end view of a shorting bar which under some conditions of operation may be inserted between two of the electrodes;

Fig. 3 is a fractional sectional view, taken on the line 33 of Fig. 2, with certain parts omitted;

Fig. 4 is a fractional sectional view taken on the line 4-4 of Fig. 2;

Fig. 5 is a plan view including parts shown in Fig. 2;

Fig. 6 is a side elevation of the operating handle of Fig. 5;

Fig. '7 is a fractional sectional view taken on the line 1-1 of Fig. 5;

Fig. 8 is a fractional sectional view taken on the line 88 of Fig. 5;

Fig. 9 is a sectional view of the clamping mechanism for the pressure-applying electrode taken on the line 9-9 of Fig. 5;

Fig. 10 is a fractional sectional elevation taken in plan on the line I 0l 0 of Fig. 9, with the member I I9 omitted;

Fig. 11 is a sectional view on enlarged scale taken in plan on the line ll|l of Fig. 9;

Fig. 12 is a sectional view taken in elevation on the line l2! 2 of Fig. 11;

Fig. 13 is a side elevation, partly in section, illustrating the parts in certain positions with respect to associated limit switches;

Fig. 13A is a fractional side elevation of one adjustable limit switch of Fig. 13;

Fig. 13B is a detailed view illustrative of the manner of operation of another of the limit switches of Fig. 13;

Fig. 13-0 is a sectional view on enlarged scale taken on the line l3c-l 3c of Fig. 13;

Figs. 14 and 15 are similar to Fig. 13 but the parts are illustrated in different positions for a better understanding of the operation of the several limit switches;

Fig. 16 is a fractional plan view taken on the line Iii-i6 of Fig. 13, illustrating the location of four of the limit switches;

Fig. 1'7 is a plan view of a modified form of a pressure electrode; and

Fig. 18 is a wiring diagram which schematically illustrates both the high-frequency oscillator and the manner in which the limit switches and other control devices are utilized in the operation of the invention as a whole.

Referring to the drawings, a simplified form said housing being secured to plate 62 as by screws. The bearing housings for the idler gears 56 and 5? may be adjusted for proper gear mesh, the plate 62 (Fig. 3) having elongated slots 61 and 68 for this purpose. The mesh of gear 58 with gear 55 is also adjustable by moving the motor assembly as a whole, suitable slots and locking screws ill being provided as best shown in Figs. 4 and 5, said slots being long enough to provide adjustment for gears of smaller or larger sizes to obtain slower or faster electrode speeds as may be required. The use of the three threaded rods 58-52 provides a geometrically stablesupport for the subassembly including the plate 26, the associated insulators, and the upper electrode or capacitor plate I8. The shaft 51a of gear 51, Figs. 2, 4, 5, and 8, extends above the motor plate 5I as a convenient means of manually turning the gear train during testing or for adjustment of limit switches.

The second or intermediate electrode i1 and its sub-assembly, including the insulators 28, 28a, 2| and 25a, and the plate 23, are secured (Fig. 2) to a vertically extending lift rod or post 12 by means of a nut is which clamps the plate 23 against a shoulder of rod 12. The lift rod I2 at its upper end is connected to a chain 14 carried on a sprocket I5, Figs. 2, 5 and '7, which in turn is supported by a shaft 16 rotatably mounted by journals 1'! and I8. The chain '14 extends (Figs. 5 and '7) over a sprocket l9, rotatably mounted with respect to a supporting shaft 85, and thence downwardly through a central opening in a counterweight 8!. Its lower end is secured to a threaded stud 82 of a second counterweight 83. The counterweights 8i and 83 cooperate, in a manner that will later be described in detail, to control the direction of the force applied and thus the direction of movement of the assembly including the plate 23 and the electrode IT. The upper counterweight BI has secured to it a pair of chains 84 and 85 (Fig. 5), which are shown in Fig. 2 as attached to threaded studs 86. The chain 85 extends over a sprocket 81 carried by the shaft 8! over a sprocket 88 carried by a shaft 89, and downwardly around a sprocket 98, one end being attached thereto by a screw extending through the down-turned link on the end of the chain 85, Fig. 8. The sprocket 98 is secured to an operating shaft 9I.

Similarly, the other chain 84 extends from the other side or end of the counterweight 8| (Fig. 5) over sprockets 92 and 93, respectively carried by shafts 8d and 89, and thence downwardly to a sprocket 98 (Fig. 4), corresponding with the sprocket 96 (Fig. 8), which of course is also secured to the operating shaft 9|. The operating shaft 9i (Figs. 4, 5, '7, and 8) is located directly beneath the shaft 39 and one end thereof extends outwardly through a wall 94 of the housing or cabinet M. A crank 55 (Figs. 4 and 5) is secured to the end of the shaft SI for actuation externally of the housing It. The counterweight 8! is thus moved under the control of the crank 95. As best shown in Fig. 4, the crank shaft 9I is journaled in bearings 96 and 91. It will also be seen in Figs. 2 and 4 that the counter-weights 8i and 83 are guided in their movement by rods I88 and MI. The rod IilI has been omitted in Fig. '7 in order not to be confused with the chain 74 which is directly in front of it. The counterweight 83 partially balances the weight of the assembly including the electrode IT. This partial bias limits the force with which I! falls when 8I is suddenly raised. It also decreases the load which the operator of the crank 95 must handle. It also decreases the load which the motor 35 must handle when moving both electrode assemblies. Movement of the counterweight 8I by means of the crank 95 thus may serve to control the movement of the assembly which includes the pressure-applying electrode I1 and its associated counterweight 83.

More specifically, the parts are illustrated (in Figs. 2, 3, 4, 5, '7 and 8) in positions corresponding with electrodes I1 and I8 at their maximum heights, and the crank located in its Y position as viewed in Fig. 6. The crank 95 will have been moved in a counterclockwise direction from the X position to the normal operating, or Y position. The shaft 9| (Fig. 8) will have been rotated in a counterclockwise direction. Since corresponding ends of the chains 84 and 85 (Figs. 4, 5 and 7) are bolted or otherwise secured to the sprockets 9i! and 98, it will be seen that that rotation thereof will lift the counterweight 8| to its illustrated position. Since the assembly, including the pressure electrode I1, is heavier than the counterweight 83, the assembly including the electrode I I will tend to descend. It may not descend because bushings 5ila-52a of plate 23 are resting on plate 25. However, if the motor 35 is now energized in a direction to lower the assembly including the electrode I8, the assembly including the electrode H which is shown resting on plate 26 will also descend. Of course, as soon as the electrode Il' rests upon the top of the dielectric material or preform I6, its movement is arrested and its associated counterweight 83 likewise comes to rest. Continued operation of the motor 35 in the same direction will continue to lower the assembly including the electrode I8, but will have no eifect upon the assembly including the electrode I'l, because the rods 50, 5|, and 52 slide freely through the bushings 58a52a in plate 23. The parts are so [proportioned that in rotating the crank from its X position to its illustrated Y position, the counterweight 3| will be raised to a height which will allow the electrode I I to be lowered until it comes to rest upon a load of any height (within the limits of the design) that may be placed upon the tray electrode I4, 'or until the bushings 5Ila-52a in its supporting plate 23 come to rest on plate 26. By this arrangement, heat may be generated in thin loads while subjected to pressure as well as to thick loads or loads having a height equal to the maximum spacing provided between electrodes I4 and Il.

Continued rotation of the crank from its Y to its Z position (Fig. 6) will of course continue to elevate the counterweight 81, but such continued movement of the counterweight has no further effect upon the apparatus. However, such rotation to the Z position applies to the electrode I? and to the dielectric material or preform It a pressure of a known and predetermined magnitude. This is accomplished by means of a weight I85 (Figs. 5, 7 and 9) slidably mounted on a lever I86 pivoted by a relatively heavy pin I0! to the frame, the lever having an operative connection with the mechanism now to be described, for applying the desired pressure to the electrode I1. It will be observed that the weight I 85 (Figs. 5, 7 and 9) may, by loosening the clamping nuts I08 and I89, be moved to any desired position along the lever I66. Up-turned sides H911 and II9b of horizontal member II9, connected to lever I86, retain the weight in a desired path of travel and also provide a con- 256i, if

" star as;

shown inFi'g. '1. 'Ihey are' also" slotte' warm;

guides .1fb th rea ed" st s"wh h'f arryjth td-"the electrode ii is coi'resp'ondinglyf dec'reased;

As shown in Fig. 7, the weight'islo'catedfirf'a position to develop a pressure somewhat greater than ZOUpQunds on the electrode I 1. InFig. 7, the lever 205 is shown ,The clamping1 member I38 (Fig. 12), is provided H I V JO WithQside projections B811 and I381) which are v with an out wardly extending pin H6 resting upon the'sur-j face of a cam l l l. The cam IlI issecured totl'ie shaft (Figs. 4. and and on the opposite side cam-l identical with caml ll ispro'vided and which the lever I50 isconstructed. It is formed :by tw o side members H5 and II6 interconnected 'byspaeers l ii, I I0, and suitable fastening screws.

The two sides are connected together by a cross member H9 (Figs; 5 and 0) whichalso carries the sides H90. and H519 for the support off'the'i' weight E05. By spacing the side members H51 and H6, a clamp-operating lever or member 120 "may be disposed in nestingrelation between them. "The member 28 ispulled by springs I22 and I2 3" against the surface of a cam IZ l disposed inter-' ward the rod 12, the other clamping member. I31" will be moved toward the rod 12 by the reactive force of the cam which is transmitted I throughthe pivotal ends I43'to the yoke come.

operating iaceiof a member I41 secured to the clamping member I38 asby. screws (Fig. 10f. withshims IflQ disp'osed between them. Upon. rotation of the lever I from its position in Fig. 7 to the position in Fig. 9, the eccentric cam" I45 is rotated in a clockwise direction. It presses directly against member I41 to move thefclamping member' I38 toward the rod 12.

received by guiding channels or grooves in the respective side pieces MI and I42. While the cam'fI IB presses the clamping member I38 toprising the side pieces MI and I42. These are secured to the clamping member I31 and move mediate the cams HI and I I3. In Fig. 7, it will be seenthat cam'l2d is holding the lever or arm 1 128 in an elevated position against the biasjof the springs i22 and I23 7 A nut and threa'ded'fj stud is provided for adjustment of the tension Since'these springs are located of spring I22. v on opposite sides of the shaft 9!, the cam I24,

when in the position shown in Fig. '7, acts" as a 7 true fulcrum, thus permitting spring I22 to be adjusted relative to spring I23 to obtain a vertical au men s the axis and clamping face of each of clamping members I3? and I38 with the axis of rod 12.

Such alignment is necessary if 12'] is to slide freely through E81 and 533 when in their unclamped positions.

Referring now to Figs. 9 and 10, it will be observed that the pivot pin I01 extends through j; the/two sides II5 and I I6 of the'lever I0 6andjf through a stationary block I26 held'by 'screwsjj I21, the heads of which'may bejcountersunk into a cross member I28 extending betweenja.

pair of blocks I29 and I30. The .blocks or sup:

porting members I29 and i3 0 (Fig. 11) are f astened as by bolts I3i' (Fig. 10) to the'rnotorsupporting plate 6| (Fig. 9) The cross meme, ber of plate 128 is provided with anenlarjged opening or recess through which extendsfthej rod 12 as wellas a thrust member 533 secured in a member I34 which is pivoted between the sides H5 and H6 by means of a pivot pin I35.

When the lever I06 is rotated in av clockwise direction around its pivot pin I01, as viewed in Fig. 9, the thrust member I33 engages th" upper face of a clamping member I31. Ther clamp also includes a second clamping member I38.' As best shown in the enlarged sectionalij view' of Figs. 11 and 12,there a re attached to the clamping member I31 two side pieces I lI and I42, as by screws.

laterally of the rod 12 and provide pivotal sup-j These members extend port for the ends M3 of an eccentric camjI45 which is rotated by movement of the lever I20.. This lever (Fig. 9) has a down-turned'end I200, which is secured to thejcam 145'" asbya s'crewjf,

I46? The face of the cam I45"engages"the"colimited by projections I39 and I40 which. extend into enlarged openings (Fig. 11) of the blocks I29 and I30. I

As the crank (Fig. 6) is "rotated from position' .Yf' toward position Z, the shaft 9| is rotated in a counterclockwise direction as "viewed in Figs. 6-9. The cam I24 first releases thejlever which, by the actionof the springs I22", and I23, is rotated in a clockwise direction to thelposition shown in Fig. 9. During its ro- 35 tation, it. sets the clamp to lock the clamping members I31 and I38 to the rod 12 in the manner abovedescribed. It will be observed (Fig. 9) that a coil spring I50 encircles the rod 12, one

end bearing against a spacer I5 I while the op posite end bears against the clamping members I31 and I38. The coil spring I50 is strong enough to support theweight of the clamping mechanism and to maintain it above, and in spaced relation with, the motor-supporting plate v6|. Continued counterclockwise rotation of the crank 95 rotates the cam H3 (Fig. 9) in a coun.

terclockwise direction to release the weight ac tuat'edLlever I06 forrotation of the latter in a clockwise direction about its stationary pivot pin I01. Since the clamps I31, I38 have been rigidly, tho-ugh frictionally, connected to the rod 12, the thrust member 'I33as actuated by the lever 106 presses downwardly on theclamping member'il31 to apply through the rod 12 the" H "resultantpressure"developed by the weight I05 and the lever I06. This pressure, of substantial and predetermined magnitude, is transmitted imm rse rod 12 through the plate 22 and the" insulators 20, 20a, and 2i, 2Ia (Fig. 2, 7 and 8) to apply the pressure to the electrode I1, which,

it willbe remembered, has previously been operated into engagement with the preform I6 (Fig? 2), The crank 95 then occupies its Z position and the apparatus. is now in condition for the application of high-frequency electrical energy to the preform hile the preform is under the" aforesaid applied pressure, which may be from below pounds to above 200 pounds. By changing the size of the weight I05, any desired pressure within a wide range may be selecte'd. I

At the'time of operation of the clamping mechanism, ,it ,will be observed that it is spacedv .above' the motorfsupporting plate.BI by means of a compression spring I50 which is strong enough to support the weight of the clamping mechanism I3'l-I38. However, after operation of the clamping mechanism to clamp the rod I2, the application of pressure from the weight I05 through the thrust member I33 overpowers the spring I and permits the rod 12 and the sub-assembly including plate 23 and electrode I I to move downwardly. Of course, no imme diate movement occurs, inasmuch as the electrode IT has already been moved into engagement with the work, other than that required for application of the pressure on the work or preform I6. If the preform I6 is hard and unyielding, there will be no movement of the electrode I1. However, as its temperature rises and as it is softened, the electrode assembly I'I-ZS will move downwardly by a predetermined amount depending upon the movement permitted by the spring I50 disposed between the bushing I5I and the clamping mechanism I3'I-I38. In a preferred application of the invention this movement was of the order of one-eighth of an inch. Accordingly, the clamping mechanism will not unduly deform and compress the load or preform IE, but it will apply a predetermined pressure to it and it will maintain that pressure so long as the preform maintains its Original shape and in the event of softening or expansion of preform I6.

By now energizing the motor 35 for rotation in one direction or the other, the upper electrode or capacitor plate I3 may be moved in either di-- rection to control the voltage applied between the electrodes I4 and I1, and in that manner to control the rate of heating of the preform I6.

At the end of the heating operation, the crank 95 will be rotated from its position Z in a clockwise direction. As it is moved toward its Y position, the cams I II and I I3 (Fig. 10), acting against the pins I I (9 and I I4, return the level" i 53 and the weight I05 to the positions shown in 9. Thereafter, the cam I24 rotates the clamping lever 52!] from the position shown in Fig. 9 to the position shown in Fig. 7, the Y position of the crank 95. In other words, the clamping mechanism is operated in the reverse sequence to unclamp the rod 12. Any downward movement that may have been produced on the clamp and rod I2 by the applied pressure was opposed by a coil spring I 50. 12, the coil spring I will be effective to return the clamping members I31 and I38 to their original positions, the'thrust member I33 having been previously elevated by lever I06 to provide for the return movement of the clamping mechamsm.

The clockwise rotation of the crank 95 and the shaft 9| from its Z position to its Y position will also be effective to lower the weight 8i by an amount which has no eifect upon the apparatus. Continued clockwise rotation of the crank 95 and the shaft 9| from the Y position toward the "X position will be effective to transfer the weight of member 8| from the chains 84 and 95 (Fi 5) to the weight 83. Since the cooperating counterweights BI and 83 are heavier than the subassembly including the electrode ll, the latter will rise as long as the crank is lowering the weight BI, and, in turn, weight 83, the limit being when the electrode I'I strikes the electrode 53, which condition may occur at any point between the Y and X position of the crank, depending upon the location of electrode I8. Additional rotation of the crank toward the X position after the electrode I1 strikes the elec- Upon unclamping of the red I 1% trode I8 is merely effective to addslack to the chains 84 and 85.

From the foregoing, it will be seen that any desired pressure may be applied by the electrode 5? to work disposed between it and the cooperating electrode Hi. This has been accomplished without providing a direct drive to the assembly including the electrode IT. This feature is of considerable value since it makes it relatively impossible for anyone to injure the mechanism, by causing excessive pressure to be applied by the electrode I1, which might and probably would occur if it were necessary to provide a direct drive.

Another feature is that the pressure can be applied to a load of any height within the limits of the design, but once applied to a given load, is effective over a very small distance (approximately This feature makes it impossible for the initial pressure to cause the electrode I! to mash a load that becomes soft when heated.

With the parts again in the positions illustrated in Fig. 2, it now will be assumed that it is desired to operate the mechanism without utilizing the pressure-applying feature. It will be observed from the right-hand portion of Fig. 2 that there is held by clips I55 and I56 a handle I51 of a shorting bar I58. While in the clips I55 and I56, the handle I5! is effective through a rod I59 to maintain closed a switch I60. A side view of the shorting bar I58 removed from the clips is shown in Fig. 2-A. It will be seen that is comprises a U-shaped member, the respective legs of which normally extend outwardly from each other. They are resilient and preferably of a copper alloy. The frame of the shorting bar is of insulating material such as hardwood.

The handle I5! is grasped and the shorting bar I58 thrust between the electrodes I! and I8. The outwardly extending arms will be depressed and, because of the wiping action incident to their insertion between plates I1 and I8, good electrical contact will be made with the electrodes. Accordingly, the circuit including the flexible conductor 44 extends from the oscillator to the electrode I8, through the shorting bar I58 and to the electrode H. The capacitor formed by electrodes or plates I! and I8 is thereby removed from the circuit. If the motor 35 (Fig. 8) be now energized, the threaded rods 50, 5i, and 52 may be rotated in a direction to lower the subassembly including the electrode I8. The assembly including the electrode I! will then follow the descent of the assembly including the electrode I8 in manner already described. By suitably controlling the energization of the motor 35, the electrode ll may be adjusted to any desired position with respect to the dielectric material such as the preform I6.

Besides providing for movement of the assembly including the electrode I? by shifting the effective and relative positions of the counterweights 5| and 83, limit switches are provided in a control system for the motor 35 to prevent the development of undue strain on any of the parts. In accordance with the invention, the limit switches are automatically effective to control the permissible movement of the upper electrode or capacitor plate I8 between predetermined limits, both of which limits may be varied by amounts within the permissible range of movement of the assembly including the intermediate electrode 57.

To prevent obscurement of parts already described, these limit switches have in general been system.

' The manner in which the several limit switches the limit switch 61.

l-kthe nma switeh-169 opehs the motor omitted from Figs. 1-12 but they have been illusa trated in Figs. l3'-l6 in-which figures otherparts of the apparatus already described have been 1 omitted the better-to show the location, function. and operation of the liinit"switches 'iorming the important components of; the position-controlling cooperate together will be dsc'ribed in connection withFig. 18 after "a briefde'scription o'f th'e limit switches in terms of'the functions they perform.

' Referring HOW to Fig: 13, a limit switcli lfil adjustably secured, as by clamping nuts 162, to an upright member 'lt3 supported from the plate 62, determines the maximum height to which the 1 motor ma'y ra'ise the capacitorassemblyinciud- 'ing the electrode "[8 andthe supporting plate 25.

As shown in Fig-{13A, the upright let is provided with anelongatedslot lfilthrough which threaded studsextend from the case or housing of Beneath-their associated Glamping'nuts'IBZ' is an index "plate H55 which cooperates wi'th'a scale*l66"which permits a setting-oi the limit switch It! to predetermine the height to which are antatagends It may 'be raised, themaximum "setting cori' espcnding with the makimuih heig'ht to which the apiparatus is designed to operate.

' The" actuator" [61, which coacts with a rollercarryin'g arni 'lfild'of-thelimit-switch I65. is supported from anangle -l"l2-'-carried by'the upper end of the threaded rod'50, which it will be recalled is driven" by the" motor 35. The upper end of the 'rod'50 is provided witha tapped hole which receivesacap" screwl 58* to clamp the angle H2 1 against the upper ra eo'r the threaded rodfifi. The angle 112 provides for-the mounting of two additional limit switches" i 69 and I It. 1

" 'InFig 14; the-electrode H and the capacitor plate or electrodeilt' are-shownin positionsmuch lower th'afi in Fig. 13 Accordingly, the actuator IE1 is belowthe actuaungarm ifila of the limit switch ltl'. Whe'n'the m'oto'rrotates'the threaded rod 50 to raise 'itj the actuator &6? moves against the'roller' of arni' [G ld to-"spec the limit switch [6| thereby tod'eene'r'gize the motor.

"The limit'switch" levees its housing secured to that of the" limit switch H9, and the two together are"secured to an upright of angle 112 *by one "or more'bolts' H3 (Fig. 16). Accordingly; these limit *switches I59 and H51 -move up and 'downwith'the"threaded rod and withthe actuator "151'." The limit switch I69 prevents the motor "from driving the capacitor plate 18 into engagement with the elecvtrode l1. Thus, ifthe rod be rotated in a direction to lower the plate [8, it will be observed the actuator ltfia (Fig. 13) will be moved toward a stationary arm We carried by a rod I15 which is secured to the plate 23 forming a part of the movable assembly which includes electrode H.

in the arm N4, the holetherethroughproviding adequate clearance for iree movement of the endof member ill has secured theretoa small plate Him-as by threaded'engagement. As the electrode I7 is lowered to the'position shown in Fig. 15, the plate l 11a of member lTl' engages the motor-supporting plate til. Though-the movement of member H! be arrested, the electrode 'l'l'may be further lowered. However, if the capacitor electrode i8 is also lowered-as by proper energization of'the motor 35, the resultant lowering of the threadedrod 50 (Fig 15) will move the limit switch H59 into engagement with the auxiliary member I'll thereby to open the motor circuit and prevent further lowering of capacitor platelfi.

By reason of the foregoing provisions great flexibility of operation is provided ancllthere' is avoided any danger of operation iofthe motor to lower the threaded rods topo'sltions below their threaded engagement with their cooperating su porting members carried by'the respective gears 53, 54, and 55. l j

Thelimit sWitCh H0 is a single-pole doublethrow switch. Its actuator l'lfiwcocperates with an arm 978 secured to the rod H5 by means of clamping nuts I19, provided 'for factoryadjustment thereof. One of the functions of the switch 5 it is to limit the upward movement of the" plate 25 with respect to the plate 23. For example, when the plate 26 is moved'upwardly from its position as shown in Fig. 14 to the pos'itionshown in Fig. 13, the limit switch I76 and its" actuator l'lila approach the arm H8 for a'ctuation of the limit switch I18 from one of its positions to the other. These will be hereinafter'referred.'to as the-actuated position 'and"the' unactuated position.

A fourth limit switch ISO is supported from the frame by'a bracket i8l (Fig; 16) so disposed that actuating member lBOa of the switch is in a position to beengaged by an actuator I82 secured to a collar 83 carried by and'sccurcd to the shaft 89. The shaft 89 is, as above described, driven through the chains '24 and 85 upon rotation of the crank (Figs.5 and fil. The actuator I82 is arranged to engage the actuating member 1853a 0f the limit switch H86 (Fig. 13') when the crank 95 (Fig. 6) is in its Y position. With the crank 95 in its other positions, the limit switch I80 will be open. By reason of these provisions, and with the crank in the Y position (Fig. 13), a circuit may be completed through the limit switch I80 for raising the capacitor plate l8 even'though the plate 26 is in engagement with the upper plate 23. In other words, the motor is theneffective to raise both subassemblies which include electrode I! and capacitor plate l8.

With the above understanding of the location of the respective limit switchesand the functions performed by each; reference may now-be'ha'd to Figs. 1316 "and 18 fora description of the operation as a whole. ln lfi i'g. 18, a high-frequency generator or oscillator 585 has been illustrated. as'includinga'vacuum tube iS', the cathode of which is heatedby connection to the secondary winding of a transformer [88 the primarywinding of which is connected to a suitable source of supply I89. There are included in the grid circuit a grid coil 1'90", agrid-leak resistor'lt Land a capacitor I92 in shunt'therewith. The anode of the vacuum tube I3! is conheated by way of a radio-frequency choke MI 75 to the positive terminall3+ of a'direct-current 13 source of supply, the-negative'terminal marked B'- being connected to ground. A suitable measuring instrument:!99 is connected in the plate or anode circuit to measure the magnitude of the current. A part of the scale of the instrument or ammeter I93 may be distinctively marked, as at I93a, for flow of current of magnitude corresponding with a normal full load output for the generator or vacuum tube I81. The output circuit includes a blocking capacitor I94, the 1.

output inductor I95 (corresponding with coil II of Fig. 1) and the capacitor formed by the plates I! and I8, as well as a second capacitor in series therewith and formed by the plates or electrodes l4 and Ill. The frequency of the oscillations produced by the generator I 96 will be determined by the values of the inductance of the inductor I95 and the capacitance in parallel therewith. While the frequency is not critical, it will generally be selected as omething above 1,000,000 i cycles per second and'in general will'be of the order of from oneto thirty megacycles per second and above. The particular frequency range desired will be selected in accordance with principleswell understood by those skilled in the art.

The motor 35 includes a field winding I96 arranged to be energized from supply lines I97. and I98. A second field winding I99, with a series resistor 299 and a series capacitor is connected to a reversing switch 282, which determines the direction of current flow through the field winding I99 for rotation of the motor in one direction or the other. Upon closure of a line switch 283, it will be observed the operating coil 294 of the reversing switch 292 is energized through a circuit which may be traced from supply line I97, line switch 293, the normally closed contacts of a lower push-button switch 295, the operating coil 20%, and to the other supply line I98. The reversing switch 292 is thereby operated to complete connections of the field winding I99 preparatory to flow of current therethrough in a direction for rotation of the motor 35 to elevate or raise the inner subassembly including the plates I8 and 26. This circuit may be completed by depressing the raise push-button switch 299. This circuit may be traced from the supply line I9'I, the line switch 293, the normally closed contacts of switch 2%, conductor 231, the

raise switch 265, limit switch I 6!, conductor 293, limit switch I19 in its unactuated position, conductors 289-2! I, contact 2 I2 of reversing switch capacitor 29!, resistor 298, field winding I98. conductors M3 and 2M, contact M5, and by conductor 9 I 6 to the supply line I93. The subassembly I929 will then be raised until either the limit switch I Si or the limit switch I I0 is operated.

Regardless of where the outer electrode assembly I'I-23 may be, as soon as the plate 26 approaches the plate 23 the limit switch I19 will be'operated from its unactuated to its actuated position to deenergize the motor 35.

If the subassembly IT -Z'B'is thereafter raised, as by operation of the crank 95, it isto be understood the limit switch I79 will be returned to: the illustrated unactuated position of, Fig. 18, thereby rendering the raise circuit eifective to energize the motor 35 further to elevate the subassembly I9-26.

If it be assumed that the subassemblies are in the positions shown in Fig. 15 and that the crank 85 is located in its Y position, the actuator I82 will have closed the limit switch I89 and will have by-passed the limit switch I'IU so far as the raise circuit is concerned. Hence, the motor 35 will'then be effective not only to raise the subassembly I825, but after engagement by the plate 26 of the bushings a52a in the plate 23, the outer subassembly I'I-23 will also be raised. The limit switch I is closed or made efiective only when the crank is in the Y position, since the electrode I! is clamped when the crank is turned toward the Z position. This provides additional flexibility since the electrode ii and the capacitor plate I 8 may both be raised without requiring operation of the crank to shift the counterweights for gravity elevation of the outer subassembly I'I29.

As has already been explained, if the crank 95 is moved from its Y position, in either direction, the limit switch I8iiis opened and the described alternative operation may not take place until the crank 95 is returned'to its Y position.

With the motor 95 energized through the limit switch I89, upward movement of both assemblies continues until the actuator IB'I engages the roller on the arm Iiiia to open the limit switch ItI,

- which of course deenergizes the motor 35. Thus,

the limit switch I91 determines the absolute height of the subassembly I8 2t and this may be adjusted as by varying the position of the limit switch IEI, as has already been explained in connection with Figs. 13 and 13-A.

Again assuming the parts are in the positions illustrated in Fig. 18, with line switch 209 closed and the coil of reversing switch 292 energized, then if the lower push-button switch 2% is depressed its normally closed contacts will be opened to deenergize the coil 204 of the reversing switch 292 which thereupon operates to its illustrated position to reverse the direction of flow of current through the field winding I99. The push-button switch 295 also closes its normally open contacts to complete an energizing circuit for the field winding I99 which may be traced from the supply line I 97 by line switch 293, conductor 2II, the now closed contacts of switch 285, limit switch 569 and I58, conductors ZIII and EH, the contact 2I8 of the reversing switch 282, conductors 2M and 2I3, field winding I99, resistor 209, capacitor 20 I, contact 2I9, and by conductor 2 It to the other supply line I98. The motor 35 thereupon rotates in a direction to lower the subassembly including the capacitor plate I8. As the plate or electrode I9 approaches the plate electrode H, the limit switch I69 will be opened. Accordingly, the motor 95 may never be energized to lower the capacitor plate I8 far enough to engage or apply pressure to electrode I I. The minimum space which will be maintained between the two plates It and I8 is determined at the factory by fixing the position of the actuator I'M on the rod I15 (Fig. 13). Since the position of the plate electrcde I! may be anythingbetween its upper and lower limits, it is to be understood that the limit switch I99 is operated not as a function of absolute height but as a function of the approach of plates I! and 13 toward each other, that is, the relative distance between them.

If it isdesired to utilize only the electrode I! without making use of the separate capacitor provided by the plate It, the shorting bar !59 is graspedby its handle I 51 and inserted between the electrode H and the capacitor plate I9. This insertion may be made only when there is maximum separation between them, as when plate 23; is caused to rest on plate 26 by turning the crank 95 to its Y position, and after operation of the limit switch 110 to its actuated position. With the shorting bar 58 in position, its flexible U-shaped form frictionally engages the two plates and, because of the resilience or elastic character of the shorting bar I53, permits some relative movement as will be hereinafter explained. By lifting the handle I51 (Fig. 2) from its supporting clips E55 and 56, the by-pass switch 469 (Fig. 18) moves to open the circuit which was above traced through it. An inspection of the wiring diagram of Fig. 18 shows that the opening of the switch Hill transfers the control of the motor 35 to the limit switch Hi Specifically, the lowering circuit may not be completed unless the limit switch l'lll is in its actuated position. But this requirement has been met, since it has already been stated that the shorting bar i353 may not be inserted between plates ll and i8 unless they are spaced apart enough to insure operation of the limit switch iii! to its actuated position.

By depressing the push-button switch 265, a lowering circuit may be completed through the limit switch H6 and the motor 35 will continue simultaneously to lower both subassemblies until the plate electrode l l engages the preform ES. When this occurs, the motor will move the plate 53 downwardly to compress the U-shaped shorting bar I58. A slight movement thereof will be adequate for operation of the limit switch lit to its illustrated unactuated position, thereby to deenergize the motor 35.

Again assuming the parts are in the positions as illustrated in Fig. 13 but with the shorting bar in place between the plates H and it. the raise push-button switch 205 will be ineffective because the limit switch 16! will be open. If after the lowering of the subassemblies it is desired to raise them again, the limit switch it! will have been i closed. However, the raise circuit will not be completed through the switch I'll} which is in its actuated position, but will be completed through the limit switch 18! which was closed when the crank was turned to its Y position for operation with the shorting bar. It should here be observed that the crank 95 is turned primarily to shift the counterweights or clamp the electrode and apply pressure. Any limit switches actuated in the process energize or deenergize the raise or lower circuits because the load, electrodes, and crank are so located that it is safe or unsafe for energization of the motor in one direction or the other.

Again returning to the simultaneous lowering of the subassemblies, after the electrode H has engaged the preform l6 and the motor has been deenergized, the crank 95 may be rotated to its Z position for operation of the clamping mechanism and the application of the weight Hi and its arm its to apply a predetermined pressure through the electrode l1 to the preform E5. The many variations in the operation, which have been explained in detail, provide a highfrequency heating apparatus of great versatility and one in which a large number of heating prob lems may be successfully solved and carried out with a minimum of time required for adjustments of the apparatus.

While a preferred form of the invention has been illustrated, it is to be understood that many variations may be made therein without departing from the scope of the appended claims. The control circuits may be either of the manually controlled type or they may include motor-controlling relays for automatically varying the position of the capacitor plate l8 to maintain substantially constant the anode current of the oscillator or vacuum tube 58?. One such relay may be included in the circuit common to the ammeter I93, with lower contacts thereof substituted for switch 205 and arranged to be closed when the anode current is below the desired value and with the raise contacts thereof substituted for the switch 286 and arranged to be closed by the relay when the anode current is above the predetermined value. Besides changes of this character, various elements such as the tray-electrode Hi may take various forms and the elec trode l'i' and the capacitor plate 18 may also have any desired configuration such as illustrated by the plate 22B of Fig. 17 where, it will be observed, the central portion is made relatively small with arms extending outwardly from the corners thereof for securement to the supporting insulators. The advantage of an electrode 22% of the type illustrated is that the central portion thereof may be made of substantially the same area as that of the preforms or other shapes of dielectric materials to be heated, and thus reduce the capacitance between the various electrodes.

Summarizing the foregoing operations, when the crank (Figs. 6 and 7) is in the X position the weights 8! and 83 are effective to raise the assembly including electrode ii. That assembly will rise until electrode Ii strikes electrode is, thus bringing it to standstill. In Figs. 2, '7 and 8 both electrode assemblies are in their uppermost positions. But as already explained for the preferred operation, the electrode I? will normally be raised only an amount to clear the pre form 55 or other work to be heated. Accordingly, the limit switch it! will be set (Figs. 13 and l3A) to predetermine the upper position of the assembly including electrode [8. assuming the parts in the positions shown in Fig. 14:, with the crank 95 in its Z position for application of pressure to electrode I? and preform l6, high-frequency energy will be applied until the preform has been heated the requisite amount. Meanwhile, under manual, semi-automatic, or fully automatic control, the motor will be positioning the electrode 8 to maintain a desired potential difference on the load or preform i6. At the end of the heating operations, the crank will be rotated from its Z position to its '1' position to release the clamping mechanism and to return the weight-applying mechanism to the position shown in Fig. '7. As this is done, the weight 8! will be lowered from its uppermost position towards the weight 83. The weight 83, for the position of the electrode H in Fig. 14', will be. well above its position as shown in Fig. '7. Thus the extent of rotation of crank 35 required to lower weight 8! onto weight 33 depends upon the position of the electrode assembiy i'l--23. The weights may engage for any position of the crank between its Y and X positions and thus their combined weight will raise the assembly including electrode I! for removal of the heated preform l6.

Since it is possible for the motor to have lowered electrode or plate i8 close to the plate ii, it will be seen the shifting of the counterweights alone may not in every case insure adequate elevation of electrode it to clear the preforms. To avoid this possibility the raise button 265 should be closed before manual operation of the crans $5. This is a simple operation for the operator and it may also be carried out by a, relay which opens the lowering circuit and which is arranged to bypass the raise push-button switch upon deenergization of the oscillator, the limit switch IGI in either case serving to open the raise circuit as electrode l1 reaches its predetermined position.

After the weight 8! has been lowered onto the weight 83, continued rotation of the crank 95 towards its X position produces slack in the connecting chains but that is all that occurs after the elevation of electrode I? into engagement with the plate or electrode l8.

It is again emphasized that while the crank is in its weight-applying Z position, the switch I80 is open so that the switch ill] is effective to prevent elevation of plate 26 into engagement with the plate 23. However, with the crank in its Y position, the switch I80 is closed and the motor 35 may then be energized to raise in unison the assemblies including electrodes ll and it. Of course when limit switch iii opens, the motor 35 is deenergized.

Since the normal and preferred operation will generally be with the plate 23 but a few inches above its position in Fig. 14 (and lower than in Fig. 13) it will be understood that when the assembly il23 is raised by the counterweights it will come to rest with the electrode I? against [8. Hence the limit switch I59 will be open and the motor may not then be energized in a direction to lower the assemblies l'l-23 and i8 26. This avoids overloading the motor and undue strain on the parts. However as soon as the crank 95 is moved towards and/ or to the Y position the counterweight 8i is lifted from the counterweight 83 and the unbalanced weight will then cause assembly |l-23 to descend. Its initial movement opens limit switch I69 thus permitting energization of the motor 35 in a direction to lower assembly i826.

It may be further pointed out that with the shorting bar I58 in position between plate electrodes H and I8, the crank 525 is kept in its Y position. The motor 35 may then raise and lower the assembly l826. The assembly Il'--23, being heavier than the counterweight 83, tends to move downwardly and the motor in moving the plate 26 against the bushings lla-52a of plate 23 raises it, the motor acting only against the unbalance weight as between assembly "-23 and the counterweight 83.

With the foregoing detailed explanation in mind, it will be readily understood that further modifications in structure and in operation may be made without departing from the scope of the appended claims.

What is claimed is:

1. A high-frequency heating system comprising a high-frequency generator including a resonant circuit, a pair of electrodes forming a capacitor in series in said circuit, means including a counterweight for moving one electrode toward or away from the other electrode for accommodation of dielectric objects to be disposed therebetween for heating, a capacitor plate spaced from one of said electrodes to form a second capacitor in series in said resonant circuit, means including a motor for varying the position of said plate with respect to said one electrode to select a desired proportion of the total available radiofrequency voltage to be applied to said objects by said electrodes, two limit switches respectively connected in circuit with said motor, one of them being efiective to deenergize the motor when said plate approaches within a predetermined distance of said one electrode and the other of which is efiective to deenergize said motor when said plate is raised a predetermined distance above said one electrode, a flexible shorting bar for disposition between said plate and said one electrode for electrically connecting said plate and said electrode together, and means including said secondnamed limit switch for deenergizing said motor upon engagement of an object to be heated by said one electrode and after a slight initial movement of said plate toward said one electrode.

2. A high-frequency heating apparatus comprising a relatively stationary electrode for supporting dielectric objects to be heated, a second electrode, means including a lever and a weight for pressing said second electrode against said work with a predetermined pressure, means mounting said weight for slidable movement along said lever to control the magnitude of said applied pressure, a capacitor plate disposed above said movable electrode, means for adjusting the position of said capacitor plate for Controlling the heating of said object during said application of pressure thereto, clamping means disposed between said lever and said second electrode, and means for engaging and disengaging said clamping means for removal of and for the application of pressure to said second electrode.

3. The combination set forth in claim 2 in which said clamping means has a means extending from it and into mechanical engagement with said second electrode, and means for operating said clamping means to interconnect said lever and said second electrode for application thereto of said pressure by said lever.

4. A high-frequency heating apparatus comprising a relatively stationary electrode, a movable electrode, insulating means connected at one end to said movable electrode, a plate joined to the opposite end of said insulating means, a rod extending upwardly from said plate, a clamping mechanism associated with said rod, means for operating said clamping mechanism into and out of clamping engagement with said rod, and pressure-applying means effective after clamping of said rod by said mechanism for applying through said rod and to said movable electrode a pressure of predetermined magnitude.

5. A high-frequency heating apparatus comprising a relatively stationary electrode, a movable electrode, an upwardly extending rod for supporting said movable electrode, a double lever arrangement disposed in operative relation with said rod, a cam for controlling the position of one of said levers, a second cam for controlling the position of the other of said levers, a clamping mechanism operable by movement of one of said levers into clamping engagement with said rod, a weight adjustably mounted on the other of said levers for pressing it against its associated cam, and means operable by movement of said last-named cam to release said last-mentioned lever for applying the pressure developed by said weight to said clamping mechanism and thence to said rod and said movable electrode thereby to develop upon objects placed between said movable and stationary electrodes a pressure of predetermined magnitude.

6. A high-frequency apparatus comprising a relatively stationary electrode, a movable electrode for engaging dielectric objects disposed between it and said stationary electrode, a rod extending upwardly from said movable electrode, a clamping mechanism surrounding said rod, means supporting said mechanism in floating relation with respect to said rod, a lever extending outwardly from said clamping mechanism for operating said mechanism into and out of clamping engagement with said rod, a cam for moving said lever in one direction, and a pair of springs for moving said lever in the opposite direction, said springs being respectively located on opposite sides or" said cam for applying forces to said lever on opposite sides of said cam of magnitude to hold said lever at a predetermined angle with respect to said clamping mechanism to prevent binding with said rod when said mechanism is out of its clamping position.

'7. The combination set forth in claim 6 in which a second lever extends outwardly from said rod, said second lever having a projection extending downwardly toward said clamping mech anism, a relatively heavy weight adjustably secured to said second lever, and a cam normally supporting said second lever and said weight but operable aiter clamping engagement of said rod by said mechanism for applying the pressure developed by said weight on said second lever to said clamping mechanism and through said rod to said movable electrode and the dielectric object disposed therebeneath.

8. A high-frequency heating apparatus comprising a relatively stationary electrode, a movable electrode, means including a counterweight for moving said movable electrode in one direction, a capacitor plate disposed above said movable electrode, means including a motor for adjusting the position of said capacitor plate with respect to said movable electrode, and means for electrically interconnecting said capacitor plate and said movable electrode for movement thereof in unison in either direction.

9. The combination set forth in claim 8 in which said interconnecting means is flexible, and means operable upon movement of said plate toward said movable electrode for stopping said motor means.

10. A high-frequency heating apparatus cornprising a relatively stationary electrode, a movable electrode disposed thereabove, means including a rod for adjustably supporting said movable electrode, a, counterweight connected to said rod to apply an upward force thereto but having insuflicint weight to lift said movable electrode, a second weight, adjustable means supporting said second weight above said counterweight, and manually operable means for lowering said second weight onto said counterweight to raise said movable electrode and operable to lift said weight from said counterweight for lowering of said movable electrode.

11. A high-frequency heating apparatus comprising a relatively stationary electrode, a movable electrode disposed thereabove, means including a rod for adjustably supporting said movable electrode, a counterweight connected to said rod to apply a liftin force thereto but having insufficient weight to lift said movable electrode, a second weight adjustably supported above said counterweight, manually operable means for lowering said second weight onto said counterweight to raise said movable electrode and operable to lift said second weight from said counterweight for lowering of said movable electrode, means associated with said rod for applying a predetermined downward pressure thereto, and means operable under the control of said manual means for rendering said pressureapplying means eiiective or ineffective, as may be. desired.

12. A high-frequency heating apparatus comprising a stationary electrode and a movable electrode between which may be disposed dielectric material to be subjected to high-frequency heating, means including a rod for adjusting the position of said movable electrode with respect to said stationary electrode, clamping mechanism disposed around said rod and comprising a clamping member On either side thereof, a cam for moving said members in opposite directions into and out of clamping engagement with said rod, a lever connected to said cam and extending outwardly therefrom, a second cam normally supporting said lever in a predetermined position, springs disposed on opposite sides of said second cam for biasing said lever for movement to a clamping position, a third cam concentrically mounted with said second cam, a second lever supported by said third cam in predetermined position, a relatively heavy weight adjustable lengthwise of said second lever, means for pivotally mounting said second lever adjacent to said rod, said second lever having means movable into engagement with said clamping mechanism after release of said second lever by said third cam, and means for rotating said second and third cams, first to release said first lever for rendering said clamping mechanism efiective and thereafter for releasing said second lever for applying the weight developed on said second lever to said rod and thence to said movable electrode and the dielectrical material disposed therebeneath.

13. A high-frequency heating apparatus comprising a stationary electrode, a movable electrode for engaging dielectric objects disposed between it and said stationary electrode, rotatable means movable through predetermined positions for controlling movement of said movable electrode toward and away from a dielectric object to be heated, a capacitor plate disposed above said electrode and forming a capacitor therewith, motor means for moving said capacitor plate relative to said movable electrode, a limit switch for stopping said motor when said capacitor plate is a predetermined distance from said movable electrode, and a by-pass switch operable when said rotatable means is in a predetermined position for rendering ineffective said limit switch for further energization of said motor simultaneously to raise said capacitor plate and said movable electrode.

14. The combination set forth in claim 13 in which there is provided a flexible shorting bar which may be placed between said plate and said movable electrode electrically to interconnect them, mounting means for said shorting bar including a normally open switch which is maintained closed when said shorting bar is in place in said mounting means, a second limit switch operable from one position to another upon separaticn of said plate and said movable electrode by a predetermined amount, said predetermined separation being required for insertion of said shorting bar between said plate and said movable electrode, said switch of said mounting means in its closed position rendering ineffective said second limit switch to openL a lowering circuit for said motor, said lowering circuit including said second limit switch for deenergizing said motor upon movement of said plate toward said, movable electrode and against the bias of said flexible shorting bar.

15. A high-frequency heating apparatus comprising a relatively stationary electrode, a movable electrode, structure movable with the movable electrode, means for efiecting application of pressure by the movable electrode on objects disposed between the electrodes for heating including a weight and a first member engageable thereby and releasably clamped to said structure, and a second member operable in one sense to efiect clamping engagement between said structure and said first member and to release said weight and in another sense to lift the weight and to unclamp said structure.

16. A high-frequency heating apparatus comprising electrodes between which dielectric objects may be disposed for heating, means including structure mechanically connected to one of said electrodes for varying the spacing between them to accommodate objects of different dimensions, a weight, and releasable clamping means interposed between said weight and said structure for application, with any required spacing of the electrodes, of a predetermined pressure to the object engaged by said electrodes for heat- 9'.

17. A high-frequency heating system comprising a relatively stationary electrode, a first movable electrode, means for biasing said movable electrode to engage an object in contact with the stationary electrode, a second movable electrode, means insulating said electrodes one from the other, driving means operable within predetermined limits to vary the distance of said second electrode from said first movable electrode and to move said second electrode beyond one of the limits to move said first movable electrode away from said stationary electrode, and means for supplying high-frequency electrical energy to said stationary electrode and said second movable electrode.

18. A high-frequency heating system comprising a lower relatively stationary electrode, an upper movable electrode biased to engage an object in contact with the stationary electrode for heating said object, structure above and movable with said movable electrode, a second movable electrode insulated irom said upper movable electrode, means for supplying high-frequency electrical energy to said stationary electrode and said second movable electrode and means for moving said second movable electrode in either direction between said structure and said upper movable electrode to vary the voltage difierence between said stationary electrode and said upper movable electrode and effective upon continued upward movement to engage said structure and to raise said upper movable electrode.

19. A high frequency heating apparatus comprising a relatively stationary electrode, a movable electrode, means for relatively moving said electrodes into engagement with work disposed therebetween, a rod for supporting one of said electrodes, a clamping mechanism operable into clamping engagement with said rod, pressureapplying means effective after engagement of said rod by said clamping mechanism for relatively moving one electrode with respect to the other and for applying pressure on the work disposed between said electrodes, and a stationary stop normally spaced from but engageable by said clamping mechanism for limiting the extent of said relative movement of said electrodes during application of said pressure, thereby to limit the extent of compression of said work by reason of the pressure applied thereto.

20. The combination set forth in claim 4 in which a spring normally supports said clamping mechanism a predetermined distance above a stationary member, said spring being strong enough to support said clamping mechanism but upon operation of said pressure applying means permitting movement of said rod and plate through a predetermined distance, thereby to limit the extent of movement of said plate dur ing which said pressure is applied to said load.

CARL E. ELLSWOR'll-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,700,408 Holt Jan. 29, 1929 1,877,918 Little Sept. 20, 1932 2,079,708 Hart May 11, 1937 2,204,617 Peel et a1 June 18, 1940 2,294,480 Rohweder et al Sept. 1, 1942 2,324,068 Crandell July 13, 1943 2,396,004 Gilbert Mar. 5, 1946 2,436,732 Rowe Feb. 24, 1948 FOREIGN PATENTS Number Country Date 556,292 Great Britain Sept. 28, 1943 OTHER REFERENCES Mittelmann, Load Rematching in Electronic Heating, Electronics, vol. 18, No. 2, February 1945. Pages 114 and 115. 

